The Lindam fireguard might work and be big enough. Think you can also add extension panels in if required. It does need two very small pieces screwing into the wall though - 4 more screws in total. It has a gate so you would be able to get in to water tree and put presents under.

i googled imaged it but ebay do small picket fence panels you could paint them white and wrap in fairy lights although getting them to stand up you would have to position against walls or nail a bit of wood onto pannels somewhere to make it freestanding.

I was the same a2inthehouse and I have some very nice ornaments I don’t want pulled off. I’m going to go with the fence idea because I done own a travel/play cot and the fence option is cheaper and it looks really nice.

We had an old fashioned prison play pen that did the job brilliantly, but, as others have said, tying it to the window handle or attaching to the wall is what you need to do. that picket fence looks pretty but isn't going to be child proof.